To date, most techniques used to study nitrogen metabolism have involved invasive chemical analysis procedures or radiolabeled isotopes. The purpose of this project was to investigate the potential of 14N NMR as a non-invasive method of monitoring nitrogen containing compounds in biological tissues. We successfully detected 14N NMR signals from the in vivo brain, leg, liver, and kidney of the rat as well as from several in vitro preparations using a specifically designed NMR probe. 14N NMR signals were identified for urea, ammonia, trimethylamines and several amino acids in these tissues. We concluded that 14N NMR is a useful technique for monitoring these compounds within intact biological tissues.